<Dogs, it would seem, know straight away that there are HR on board and don't stop howling.>
Yes- this is strange. I've had several dogs and they've all been very 'disturbed' in the presence of dead things and greatly relieved to get away. They definitely understand a lot more than we give them credit for.
This is not a word of a lie. We transitted Perth Australia in a Classic 747 with a dog in the hold. Whilst doing our checks, probably not the brightest loader in the world appeared on the Flight Deck and asked the Captain: "Captain, this radioactive package has got written on it 'not in the same hold as livestock', and we've got a dog in the hold. Can we store it on the Flight Deck?". One of only 2 occasions in my life when I have been totally unable to speak.